Faster, more accurate test for salmonella

A researcher hopes a new laboratory test will help the poultry industry find salmonella bacteria in chicken and eggs before they get to market.
The test is not only much faster than traditional methods, it detects only live salmonella, which should result in fewer unnecessary recalls of poultry.
There are about 40,000 reported cases of salmonella-related food poisoning in the U.S. every year, according to the Centers for Disease Control and Prevention.

Nov 22, 2010

There is such a thing as a bad egg, and it often has to do with salmonella.

A University of Missouri researcher hopes a new laboratory test will help the poultry industry find salmonella bacteria in chicken and eggs before they get to market.

The test is not only much faster than traditional methods, it detects only live salmonella, which should result in fewer unnecessary recalls of poultry.

“The advantage of this method is that it’s rapid, so you can get the results within 12 hours versus five days with the traditional method,” said Azlin Mustapha, associate professor of food science at the MU College of Agriculture, Food and Natural Resources.

“DNA-based methods are available right now that can get the company results in a shorter amount of time, but these methods do not differentiate between the live and the dead salmonella,” she said. “Live salmonella are the ones that can kill consumers, not the dead ones, but false positives can result in a large number of unnecessary food recalls.”

There are about 40,000 reported cases of salmonella-related food poisoning in the U.S. every year, according to the Centers for Disease Control and Prevention. While most victims suffer from diarrhea, vomiting, fever and abdominal cramps, severe cases spread from the intestines to the bloodstream and can cause death. The CDC estimates that about 400 people die each year with acute salmonellosis.

New detection and measurement

The new test was developed by Mustapha and MU graduate student Luxin Wang. Their process modifies an existing technique called polymerase chain reaction (PCR), which zeroes in on pieces of DNA from a specific organism, such as salmonella bacteria, and multiplies that DNA by several orders of magnitude, generating thousands to millions of copies, making it easier to detect and accurately measure.

Mustapha’s modification adds a dye to the food sample before it is tested. The dye can’t penetrate live cells, but it can enter dead cells, where it binds to DNA molecules, making them insoluble and therefore invisible to PCR tests.

This process mirrors one that Mustapha developed to detect E. coli in beef in 2009. That test currently is used by the Missouri Department of Agriculture testing laboratory and the USDA Food Safety and Inspection Service has showed interest in it.

“The technique can allow the poultry industry accurately and rapidly test for contamination before the product is shipped,” Mustapha said. “For elderly and immunocompromised individuals, this is very important because they are sensitive and more susceptible.”